A common linear ramp generator or triangular wave signal generator charges a capacitor by a constant current source. An output signal of the linear ramp generator or the triangular wave signal generator is then compared with a reference voltage on a comparator, and a signal at an output end of the comparator is obtained to control switching of the current source. However, due to non-ideal manufacturing factors, such as stray effects and offset effects, the linearity of produced signals are affected.
In the prior art, for example, “Linearity enhancement technique of ramp generator for ADC testing” published by Chun Wei Lin on IEICE Electronics Express, discloses a method for eliminating the stray effect. The above disclosure includes a current source, a physical capacitor, a capacitor stray component and a negative impedance converter. Through charging/discharging the physical capacitor by the current source, a signal and a capacitor stray component causing a stray effect are resulted. Further, a negative matching impedance that matches the capacitor stray component is designed in the negative impedance converter to compensate the stray effect.
The negative matching impedance is obtained on a premise that an operational amplifier in the negative impedance converter is in ideal conditions. However, in practical situations, the operational amplifier may be non-ideal, leading to an inaccurate negative matching impedance that fails to match the capacitor stray component in a way that non-linearity in the output signal is caused. Therefore, it is a goal of associated industrialists to provide a solution for further calibrating the negative matching impedance and outputting linear signals.